1. Field of the Invention
The present invention relates to a grinding process for a material size reduction process based on the particle size, and more particularly, it concerns an improved classifier assembly for a rotary coal pulverizer.
2. Background of the Related Art
In operations that use coal for fuel, finely-ground coal particles or “fines” are required for efficient operation, yielding higher combustion efficiency than stoker firing, as well as rapid response to load changes. Using coal fines for combustion also produces less nitrous oxide (NOx) emissions and keeps oversized loss-on-ignition (LOI) unburned coal particles from contaminating the marketable ash byproduct of the combustion chamber. Thus, it is common practice to supply raw coal to a device, such as a pulverizer, that will reduce the size of the coal to particles within a desirable range prior to being used for combustion.
Many pulverizers employ systems and methods including one or more crushing and grinding stages for breaking up the raw coal. Coal particles are reduced by the repeated crushing actions of rolling or flailing elements to dust fine enough to become airborne in an air stream swept through the pulverizer. The dust particles are entrained in the air stream and carried out for combustion.
It should be readily apparent that the process of reducing solid coal to acceptably sized fines requires equipment of high strength and durability. Therefore, there exists a continuing need for crushing and grinding components which can reduce solid coal to acceptably sized fines in less time with greater efficiency, and in a manner which results in less wear and tear.